In the Wall Street Journal, David B. Rivkin, Jr. and Lee A. Casey argue today that with the individual mandate in Obamacare now known as a tax rather than a penalty, it is vulnerable to a new constitutional argument:

ObamaCare provides that low-income taxpayers, who are nevertheless above the federal poverty line, can discharge their mandate-tax obligation by enrolling in the new, expanded Medicaid program, which serves as the functional equivalent of a tax credit. But that program will not now exist in every state because, as a matter of federal law, states can opt out. The actual tax burden will not be geographically uniform as the court’s precedents require.

The geographic uniformity to which Rivkin and Casey refer is required by Article I, Section 8, which says that every species of tax not considered a “direct” tax must be “uniform throughout the United States.” In the paragraph just prior to the one quoted above, the authors quote the Head Money Cases of 1884, which held (though one might read this as dicta, for reasons I won’t go into here) that a “tax is uniform when it operates with the same force and effect in every place where the subject of it is found.”

But it’s not at all clear that the choice of a state to opt out of a program that would make the alternative to paying the tax cheaper, or relieve affected persons of the taxpaying obligation altogether, renders the federal tax geographically non-uniform for constitutional purposes. All persons similarly situated–unable or unwilling to purchase health insurance, while obligated either to do so or to pay a tax–will be subject to the tax. The reasons for their being subject to the tax may be partly in the power of the state governments where they live–and the authority of states to make a choice that costs them something may itself be authorized by federal law–but that does not necessarily mean that the federal government has used its taxing power in a non-uniform manner. In the Head Money ruling itself, the Court held that the tax in question (if it really was a tax, and not an exercise of the commerce power–oh, how the world turns), a 50-cent charge on foreign passengers entering the country at American seaports, was not invalid by virtue of its not applying to foreigners entering the country over land by rail. “[T]he law applies to all ports alike,” the Court observed, and added: “Perfect uniformity and perfect equality of taxation, in all the aspects in which the human mind can view it, is a baseless dream, as this court has said more than once.”

Far more promising, I think, is the approach now being attempted by the attorney general of Oklahoma, as reported by Jillian Kay Melchior at NRO today. Oklahoma, having opted out of the creation of a state-run health insurance exchange, is now relying on the statutory language of Obamacare itself (not a constitutional argument) to argue that individual citizens, and employers in the state, are completely free of the obligation to pay any of the taxes or penalties for forgoing insurance. The IRS appears to be ready to impose a tax for which there is no basis in the statute in states like Oklahoma–and many others. Challenging the mandate in this way looks more probable of success, to me, than the Rivkin-Casey argument on the Constitution’s uniformity clause.